ParameterExpression
class qiskit.circuit.ParameterExpression(symbol_map, expr, *, _qpy_replay=None)
Bases: object
ParameterExpression class to enable creating expressions of Parameters.
Create a new ParameterExpression.
Not intended to be called directly, but to be instantiated via operations on other Parameter or ParameterExpression objects. The constructor of this object is not a public interface and should not ever be used directly.
Parameters
- symbol_map (Dict[Parameter, [ParameterExpression, float, or int]]) – Mapping of
Parameterinstances to thesympy.Symbolserving as their placeholder in expr. - expr (sympy.Expr) – Expression of
sympy.Symbols.
Attributes
parameters
Returns a set of the unbound Parameters in the expression.
Methods
abs
arccos
arcsin
arctan
assign
assign(parameter, value)
Assign one parameter to a value, which can either be numeric or another parameter expression.
Parameters
- parameter (Parameter) – A parameter in this expression whose value will be updated.
- value (ParameterExpression |float) – The new value to bind to.
Returns
A new expression parameterized by any parameters which were not bound by assignment.
Return type
bind
bind(parameter_values, allow_unknown_parameters=False)
Binds the provided set of parameters to their corresponding values.
Parameters
- parameter_values (dict) – Mapping of Parameter instances to the numeric value to which they will be bound.
- allow_unknown_parameters (bool) – If
False, raises an error ifparameter_valuescontains Parameters in the keys outside those present in the expression. IfTrue, any such parameters are simply ignored.
Raises
-
- If parameter_values contains Parameters outside those in self. - If a non-numeric value is passed in parameter_values.
-
- If binding the provided values requires division by zero.
Returns
A new expression parameterized by any parameters which were not bound by parameter_values.
Return type
conjugate
cos
exp
gradient
gradient(param)
Get the derivative of a parameter expression w.r.t. a specified parameter expression.
Parameters
param (Parameter) – Parameter w.r.t. which we want to take the derivative
Returns
ParameterExpression representing the gradient of param_expr w.r.t. param or complex or float number
Return type
is_real
log
numeric
numeric()
Return a Python number representing this object, using the most restrictive of int, float and complex that is valid for this object.
In general, an int is only returned if the expression only involved symbolic integers. If floating-point values were used during the evaluation, the return value will be a float regardless of whether the represented value is an integer. This is because floating-point values “infect” symbolic computations by their inexact nature, and symbolic libraries will use inexact floating-point semantics not exact real-number semantics when they are involved. If you want to assert that all floating-point calculations were carried out at infinite precision (i.e. float could represent every intermediate value exactly), you can use float.is_integer() to check if the return float represents an integer and cast it using int if so. This would be an unusual pattern; typically one requires this by only ever using explicitly Rational objects while working with symbolic expressions.
This is more reliable and performant than using is_real() followed by calling float or complex, as in some cases is_real() needs to force a floating-point evaluation to determine an accurate result to work around bugs in the upstream symbolic libraries.
Returns
A Python number representing the object.
Raises
TypeError – if there are unbound parameters.
Return type
sign
sin
subs
subs(parameter_map, allow_unknown_parameters=False)
Returns a new Expression with replacement Parameters.
Parameters
- parameter_map (dict) – Mapping from Parameters in self to the ParameterExpression instances with which they should be replaced.
- allow_unknown_parameters (bool) – If
False, raises an error ifparameter_mapcontains Parameters in the keys outside those present in the expression. IfTrue, any such parameters are simply ignored.
Raises
- If parameter_map contains Parameters outside those in self. - If the replacement Parameters in parameter_map would result in a name conflict in the generated expression.
Returns
A new expression with the specified parameters replaced.
Return type
sympify
sympify()
Return symbolic expression as a raw Sympy or Symengine object.
Symengine is used preferentially; if both are available, the result will always be a symengine object. Symengine is a separate library but has integration with Sympy.
This is for interoperability only. Qiskit will not accept or work with raw Sympy or Symegine expressions in its parameters, because they do not contain the tracking information used in circuit-parameter binding and assignment.